A topological perspective on weather regimes
Climate Dynamics Springer 60:5-6 (2022) 1415-1445
Abstract:
It has long been suggested that the mid-latitude atmospheric circulation possesses what has come to be known as ‘weather regimes’, loosely categorised as regions of phase space with above-average density and/or extended persistence. Their existence and behaviour has been extensively studied in meteorology and climate science, due to their potential for drastically simplifying the complex and chaotic mid-latitude dynamics. Several well-known, simple non-linear dynamical systems have been used as toy-models of the atmosphere in order to understand and exemplify such regime behaviour. Nevertheless, no agreed-upon and clear-cut definition of a ‘regime’ exists in the literature, and unambiguously detecting their existence in the atmospheric circulation is stymied by the high dimensionality of the system. We argue here for an approach which equates the existence of regimes in a dynamical system with the existence of non-trivial topological structure of the system’s attractor. We show using persistent homology, an algorithmic tool in topological data analysis, that this approach is computationally tractable, practically informative, and identifies the relevant regime structure across a range of examples.Quantifying climate model representation of the wintertime Euro-Atlantic circulation using geopotential-jet regimes
Weather and Climate Dynamics Copernicus Publications 3:2 (2022) 505-533
Exploring Pathways to More Accurate Machine Learning Emulation of Atmospheric Radiative Transfer
Journal of Advances in Modeling Earth Systems American Geophysical Union (AGU) 14:4 (2022)
Interpretable Deep Learning for Probabilistic MJO Prediction
Copernicus Publications (2022)
Clarifying the role of ENSO on Easter Island precipitation changes: Potential environmental implications for the last millennium
Paleoceanography and Paleoclimatology 37:12 (2022) e2022PA004514
Abstract:
El Niño Southern Oscillation (ENSO) events yield precipitation deficits and ensuing droughts, often damaging regional forests, in many parts of the world. The relative roles of ENSO, other natural climate changes, and anthropogenic factors on the forest clearing of Easter Island over the last millennium are still debated. Here, we analyze Easter Island precipitation changes using in situ, satellite-derived and reanalysis products spanning the last 4–7 decades, and 46 monthly 156-year-long (1850–2014) simulations derived from 25 CMIP5 and 21 CMIP6 (Coupled Model Intercomparison Project phases 5 and 6) General Circulation Models. Our analysis shows that La Niña events, the cold phases of ENSO, cause precipitation deficits of −0.2 to −0.3 standard deviation (relative to long-term mean) in all analyzed data types. ENSO-like events are further examined over the last millennium (850–1981). A new multiproxy reconstruction of the NINO3.4 index based on proxy records from the Past Global Changes 2k database and Random Forest method is produced. Our reconstruction reveals unusual high recurrences of La Niña-like situations during the fifteenth to seventeenth centuries, which likely induced significant precipitation deficits on the island. These situations are compared to published vegetation reconstructions based on pollen analyses derived from sedimentary cores collected in three island sites. We conclude the environmental consequences of cumulative precipitation deficits over long-lasting La Niña-like situations reconstructed here over the fifteenth to seventeenth centuries were likely favoring drought and forest flammability. La Niña events should be better accounted for among the causes of forest clearing on Easter Island.